Cisco 7604 Configuration Guide - Page 104
Monitoring SYN Attacks in Contexts
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Managing Security Contexts Chapter 4 Configuring Security Contexts Xlates 8526 8966 93400 0 Summary Hosts 254 254 262144 0 Summary Conns [rate] 270 535 42200 1704 Summary Fixups [rate] 270 535 100000(S) 0 Summary U = Some contexts are unlimited and are not included in the total. S = System limit: Combined context limits exceed the system limit; the system limit is shown. The following is sample output from the show resource usage system counter all 0 command, which shows the resource usage for all contexts, but it shows the system limit instead of the combined context limits: hostname# show resource usage system counter all 0 Resource Telnet SSH ASDM IPSec Syslogs [rate] Conns Xlates Hosts Conns [rate] Fixups [rate] Mac-addresses Current 0 0 0 0 0 0 0 0 0 0 0 Peak 0 0 0 0 0 0 0 0 0 0 0 Limit 100 100 80 10 30000 1000000 262144 262144 170000 100000 65535 Denied Context 0 System 0 System 0 System 0 System 0 System 0 System 0 System 0 System 0 System 0 System 0 System Monitoring SYN Attacks in Contexts The FWSM prevents SYN attacks using TCP Intercept. TCP Intercept uses the SYN cookies algorithm to prevent TCP SYN-flooding attacks. A SYN-flooding attack consists of a series of SYN packets usually originating from spoofed IP addresses. The constant flood of SYN packets keeps the server SYN queue full, which prevents it from servicing connection requests. When the embryonic connection threshold of a connection is crossed, the FWSM acts as a proxy for the server and generates a SYN-ACK response to the client SYN request. When the FWSM receives an ACK back from the client, it can then authenticate the client and allow the connection to the server. You can monitor the rate of attacks for individual contexts using the show perfmon command; you can monitor the amount of resources being used by TCP intercept for individual contexts using the show resource usage detail command; you can monitor the resources being used by TCP intercept for the entire system using the show resource usage summary detail command. The following is sample output from the show perfmon command that shows the rate of TCP intercepts for a context called admin: hostname/admin# show perfmon Context:admin PERFMON STATS: Xlates Connections TCP Conns UDP Conns URL Access URL Server Req WebSns Req TCP Fixup HTTP Fixup FTP Fixup AAA Authen Current 0/s 0/s 0/s 0/s 0/s 0/s 0/s 0/s 0/s 0/s 0/s Average 0/s 0/s 0/s 0/s 0/s 0/s 0/s 0/s 0/s 0/s 0/s 4-40 Catalyst 6500 Series Switch and Cisco 7600 Series Router Firewall Services Module Configuration Guide using ASDM OL-20748-01
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